I have output :

-((Ctot (-1 + E^((-kb - kf) t)) kb)/(kb + kf))

how can I change to form

((Ctot (1 - E^((-kb - kf) t)) kb)/(kb + kf))

so forcing the minus into the bracket.

  • $\begingroup$ The first form has a smaller LeafCount, so for MMA it's simpler and hence it will choose this form. $\endgroup$
    – corey979
    Commented Oct 20, 2016 at 18:54

1 Answer 1


A substitution involving HoldForm can give the appearance that you request

expr = -((Ctot (-1 + E^((-kb - kf) t)) kb)/(kb + kf));
expr /. -1 + u_ :> -HoldForm[1 - u]

Onward manipulation may require the use of ReleaseHold.

I frequently find this approach useful.

  • $\begingroup$ Thank you, that worked perfectly. I required to implement ReleaseHold.as you mentioned! :-) $\endgroup$
    – SPIL
    Commented Oct 26, 2016 at 15:57

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